From: Richard Henderson <rth@twiddle.net>
To: Alexander Graf <agraf@suse.de>, QEMU Developers <qemu-devel@nongnu.org>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Subject: Re: [Qemu-devel] [PATCH] x86: only allow real mode to access 32bit without LMA
Date: Sat, 07 Dec 2013 06:46:46 +1300 [thread overview]
Message-ID: <52A20D86.8050300@twiddle.net> (raw)
In-Reply-To: <1386334344-24620-1-git-send-email-agraf@suse.de>
On 12/07/2013 01:52 AM, Alexander Graf wrote:
> When we're running in non-64bit mode with qemu-system-x86_64 we can
> still end up with virtual addresses that are above the 32bit boundary
> if a segment offset is set up.
>
> GNU Hurd does exactly that. It sets the segment offset to 0x80000000 and
> puts its EIP value to 0x8xxxxxxx to access low memory.
>
> This doesn't hit us when we enable paging, as there we just mask away the
> unused bits. But with real mode, we assume that vaddr == paddr which is
> wrong in this case. Real hardware wraps the virtual address around at the
> 32bit boundary. So let's do the same.
>
> This fixes booting GNU Hurd in qemu-system-x86_64 for me.
>
> Reported-by: Michael Tokarev <mjt@tls.msk.ru>
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
> target-i386/helper.c | 6 ++++++
> 1 file changed, 6 insertions(+)
Reviewed-by: Richard Henderson <rth@twiddle.net>
r~
next prev parent reply other threads:[~2013-12-06 17:47 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-06 12:52 [Qemu-devel] [PATCH] x86: only allow real mode to access 32bit without LMA Alexander Graf
2013-12-06 17:46 ` Richard Henderson [this message]
2013-12-06 18:48 ` Michael Tokarev
2013-12-06 18:57 ` Stefan Weil
2013-12-07 18:49 ` Michael Tokarev
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